Multi-Layer Electronic Component and Method for Manufacturing the Same, Multi-Layer Piezoelectric Element

ABSTRACT

In order to provide a multi-layer electronic component in which the occurrence of delamination between the ceramic layer and the internal electrode is restricted and a method for manufacturing the same, the multi-layer electronic component of the present invention comprises a stack formed by stacking piezoelectric layers and internal electrodes one on another alternately and a pair of external electrodes formed on two opposing side faces of the stack, wherein the internal electrode consists of a first internal electrode connected to the external electrode formed on one of the two side faces and a second internal electrode located between the first internal electrode and connected to the external electrode formed on the other one of the two side faces, and wherein the internal electrodes and the piezoelectric layers are faced in proximity so that a space between them is 2 μm or less over an area occupying 50% or more of the active region where the first internal electrode and the second internal electrode oppose each other.

TECHNICAL FIELD

The present invention relates to a multi-layer electronic component anda method for manufacturing the same, and particularly to a multi-layerpiezoelectric element and an injection apparatus constituted by usingthe element. More particularly, the present invention relates to amulti-layer piezoelectric element used for fuel injection apparatus ofautomobile engine, liquid ejecting apparatus of ink jet printer or thelike or a drive unit used in precision positioning device or vibrationpreventing device for an optical apparatus, or to a multi-layerpiezoelectric element used as a sensor element mounted in combustionpressure sensor, knocking sensor, acceleration sensor, load sensor,ultrasonic sensor, pressure sensor, yaw rate sensor or the like, or usedas a circuit component mounted in piezoelectric gyro, piezoelectricswitch, piezoelectric transformer, piezoelectric breaker or the like.

BACKGROUND ART

Use of multi-layer piezoelectric element made by alternately stackingpiezoelectric layers and internal electrodes, for example, has beenproposed for constituting a multi-layer electronic component in order toachieve a large displacement by making use of electrostrictive effect.The multi-layer piezoelectric element can be divided into twocategories: fired-at-once type and stacked type where piezoelectricporcelain and internal electrode sheet are stacked one on anotheralternately. When the requirement to reduce the voltage andmanufacturing cost are taken into consideration, the multi-layerpiezoelectric element of fired-at-once type is more advantageous inorder to decrease the layer thickness.

The multi-layer piezoelectric element of fired-at-once type is madesimilarly to a multi-layer ceramic capacitor by forming an activesection by stacking green sheets that include a piezoelectric materialand internal electrode sheet that includes an internal electrodematerial, forming an inactive section by stacking a plurality of theceramic green sheets on the top and bottom surfaces of the activesection, and degreasing and firing the stack.

In recent years, such a practice has been becoming common that a compactmulti-layer piezoelectric actuator is operated continuously over anextended period of time with an electric field of higher intensity beingapplied thereto, in order to obtain a larger displacement under a highpressure.

In order to meet such a requirement, a multi-layer electronic componentdisclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-299588has column-like portion formed in an internal electrode layer from amaterial, that includes 10 to 20% of piezoelectric ceramic powder ofwhich particle size is controlled within a range form to 1 times thethickness of the internal electrode, so as to bridge between ceramiclayers, thereby to prevent delamination of the internal electrode andthe ceramic layer after firing.

However, in the multi-layer electronic component disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 4-299588, because of slow rateof cooling down after heat treatment in the process of connecting theinternal electrode and an external electrode, there is a gap generatedbetween the internal electrode and the ceramic layer over substantiallythe entire interface thereof in an area where column-like portion 51 isnot formed, due to a difference in thermal expansion between theinternal electrode 102 and the ceramic layer 101 as shown in FIG. 5,with the gap T larger than 2 μm in 50% or more of the entire interface.As a result, there has been such a problem that continuous operationover a long period in high electric field leads to delamination.

In a multi-layer electronic component disclosed in Japanese UnexaminedPatent Publication (Kokai) No. 5-217796, occurrence of micro cracks thatare generated during cutting and may cause shorting is prevented bysubjecting a cut surface (external electrode forming surface) formed bymechanical processing of the device to a heat treatment that is appliedat a temperature higher than that of the first firing.

However, because of a slow rate of cooling down carried out after theheat treatment applied at a temperature higher than the firingtemperature, there has been peel-off occurring over substantially theentire interface thereof due to a difference in thermal expansionbetween the internal electrode and the ceramic layer. As a result, therehas been such a problem that continuous operation over a long period inhigh electric field leads to delamination.

FIG. 7 shows a multi-layer piezoelectric element disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 61-133715, which isconstituted from a stack 200 and external electrodes 223 formed on apair of side faces that oppose each other. While the stack 200 is formedby stacking piezoelectric material 221 and internal electrode 222 one onanother, the internal electrode 222 is not formed over the entireprincipal surface of the piezoelectric material 221, in a so-calledpartial electrode structure. The piezoelectric material is stacked suchthat the internal electrode 222 is placed in every other layer in astaggered manner so as to be exposed alternately at the left then at theright on different side faces of the stack 200. Then the externalelectrodes 223 are formed so that the internal electrodes 222 that areexposed to the pair of opposing side faces of the stack 200 areconnected to each other, thereby connecting the internal electrodes 222in every other layer.

The multi-layer piezoelectric element of the prior art may bemanufactured by printing an internal electrode paste in the pattern of apredetermined electrode structure on a ceramic green sheet that includesthe material of the piezoelectric material 221, stacking a plurality ofthe green sheets coated with the internal electrode paste so as to forma multi-layer green compact and firing the green compact thereby to makethe stack 200. Then the external electrodes 23 are formed by firing on apair of side faces of the stack 200, thereby to make the multi-layerpiezoelectric element.

The internal electrode 222 is formed from an alloy of silver andpalladium and, in order to fire the piezoelectric material 221 and theinternal electrode 222 at the same time, composition of metals includedin the internal electrode 222 was set to 70% by weight of silver and 30%by weight of palladium (refer to, for example, Japanese UnexaminedUtility Model Publication (Kokai) No. 1-130568).

The internal electrode 222 is made of metal composition that includessilver-palladium alloy instead of pure silver because, when a voltage isapplied between the pair of opposing internal electrodes 222 that aremade of silver without palladium content, the so-called silver migrationoccurs in which silver atoms of the pair of internal electrodes 222propagate along the device surface from the positive electrode to thenegative electrode. Silver migration occurs conspicuously in anatmosphere of high temperature and high humidity.

In case a multi-layer piezoelectric element of the prior art is used asa piezoelectric actuator, it may be provided with lead wires (not shown)soldered onto the external electrodes 223 and operated by applying apredetermined voltage between the external electrodes 223. In recentyears, since it is required to make a compact multi-layer piezoelectricelement capable of achieving a large amount of displacement under a highpressure, continuous operation is carried out over a long period with ahigher electric field applied.

Such a multi-layer piezoelectric element of fired-at-once type asdescribed above is required to equalize the temperature at which theinternal electrode 222 is sintered and the temperature at which thepiezoelectric material 221 is sintered, and compositions of thematerials used to form the internal electrode 222 and the piezoelectricmaterial 221 have been studied. However, since this allows residualstress caused by the difference in thermal expansion between theinternal electrode and the ceramic layer to be concentration in thecrystal grains of the piezoelectric material 221 that faces the internalelectrode 222, there has been such a problem that delamination occurs inwhich the internal electrode 222 peels off the piezoelectric material221 during operation when the device is used as an actuator.

Particularly when those among the crystal grains of the piezoelectricmaterial 221 that face the internal electrode 222 are small, suchtroubles occur as the value of dielectric constant becomes smaller thanthat of larger grains of the same composition due to the size effect,and the amount of piezoelectric displacement becomes smaller. Even whenaverage crystal grain size of the crystal grains of the piezoelectricmaterial 221 is made larger, if there are grains having small amount ofpiezoelectric displacement among the crystal grains of the piezoelectricmaterial 221 that faces the internal electrode 222, smaller amount ofdisplacement than that of the crystal grains of the piezoelectricmaterial 221 during operation causes the residual stress generated dueto the difference in thermal expansion between the internal electrode222 and the ceramic layer 221 to be concentrated at one point thusmaking an initiating point for cracks and delamination.

There has also been such a problem that the mount of displacement variesdue to the occurrence of delamination. When the rate of occurrence ofdelamination becomes higher, temperature of the device increases. Whenthe heat generated by the device exceeds the heat that can be removed bydissipation, thermal excursion occurs, resulting in breakage and suddenfailure to achieve the required amount of displacement. Therefore, therehas been a demand for internal electrodes having lower specificresistance in order to suppress the device temperature from rising.

However, specific resistance of the silver-palladium alloy that has beenused in the prior art is higher than that of a single-element metal suchas silver or palladium depending on the composition of the alloy. Forexample, silver-palladium alloy including 70% by weight of silver and30% by weight of palladium has specific resistance 1.5 times as high asthat of palladium. Moreover, lower sintering density of the internalelectrode 222 results in even higher resistance, thus posing alimitation to decreasing the specific resistance of the internalelectrode 222.

When the conventional multi-layer piezoelectric element is used as anactuator for driving a fuel injection apparatus or the like as describedabove, there is a problem that the amount of displacement graduallychanges resulting in malfunction of the apparatus. Therefore, it hasbeen called for to suppress the amount of displacement from changing andimprove durability during continuous operation over a long period.

For a multi-layer piezoelectric element, it is a common practice tocarry out polarization treatment by applying a voltage of about 1 kV(refer to, for example, Japanese Unexamined Patent Publication (Kokai)No 2002-293625). Specifically, in the polarization treatment disclosedin Japanese Unexamined Patent Publication (Kokai) No. 2002-293625, themulti-layer piezoelectric element having the external electrodes formedthereon is (1) immersed in a heated oil bath, (2) subjected to a voltageapplied thereto, and (3) cooled down after decreasing the voltage.

However, in the polarization treatment disclosed in Japanese UnexaminedPatent Publication (Kokai) No. 2002-293625, there is a problem that thecrystal grains that constitute the piezoelectric material cannot undergofully saturated polarization and, for example, particularly the amountof displacement among the piezoelectric characteristics decreases in anoperation test conducted over a long period of time. This is because thedegree of orientation of the crystal grains of the piezoelectricmaterial changes more significantly through operation.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the problems describedabove, and has an object of providing a multi-layer electronic componentin which the occurrence of delamination between the ceramic layer andthe internal electrode is restricted and a method for manufacturing thesame.

Particularly, it is an object of the present invention is to provide amulti-layer piezoelectric element that has excellent durability in whichdelamination is restricted from occurring during operation and theamount of displacement does not vary even when the piezoelectricactuator is subjected to continuous operation over a long period under ahigh voltage and a high pressure, and an injection apparatus using thesame.

Another object of the present invention is to provide a multi-layerpiezoelectric element wherein crystal grains of the piezoelectricmaterial experience less change in the degree of orientation throughoperation so that the piezoelectric characteristics undergo lessdegradation in an operation test over a long period of time and a methodfor manufacturing the same, and an injection apparatus using the same.

In order to achieve the objects described above, the multi-layerelectronic component of the present invention comprises a stack formedby stacking piezoelectric layers and internal electrodes one on anotheralternately and a pair of external electrodes formed on two opposingside faces of the stack, wherein the internal electrode consists of afirst internal electrode connected to the external electrode formed onone of the two side faces and a second internal electrode locatedbetween the first internal electrode and connected to the externalelectrode formed on the other one of the two side faces, and wherein theinternal electrodes and the piezoelectric layers are faced in proximityso that a space between them is 2 μm or less over an area occupying 50%or more of the active region where the first internal electrode and thesecond internal electrode oppose each other.

The region where the first internal electrode and the second internalelectrode oppose each other is a portion which performs the function ofthe multi-layer electronic component, and will be referred to as anactive region or active section in this specification. One of the firstinternal electrode and the second internal electrode is a positiveelectrode and the other is a negative electrode.

In the multi-layer electronic component of the present invention, it ispreferable that change in the degree of orientation of the crystalgrains that constitute the piezoelectric layer is limited to within 5%after repeated operations.

By restricting the change in the degree of orientation of the crystalgrains that constitute the piezoelectric layer through operation to notmore than 5%, degradation in piezoelectric characteristics, particularlythe amount of displacement, can be made small after operation over along period of time, thus ensuring high reliability.

In case the ceramic layer is formed from the piezoelectric material, thecrystal grains of the piezoelectric layer preferably have average grainsize of 2.5 μm or less. The crystal grains that constitute thepiezoelectric layer having average grain size of 2.5 μm or less can havethe degree of orientation of the crystal grains increased by thepolarization treatment, and the change in polarizability can be furtherdecreased.

The multi-layer piezoelectric element of the present invention whereinthe ceramic layer is formed from a piezoelectric material experiencesless deterioration after repetitive operations of more than 10⁹ cyclesunder such conditions as, for example, load of 150 kgf, temperature of150° C. and frequency of 50 Hz, and has sufficient performanceapplicable to an injection apparatus that requires high reliability incontinuous operation.

In case the ceramic layer is formed from the piezoelectric material,thickness of the piezoelectric layer is preferably 200 μm or less, whichenables it to apply sufficiently high electric field in the direction ofthickness, thus allowing it to carry out saturation polarization.

Thickness of the internal electrode is preferably 5 μm or less in orderto achieve higher conductivity in the direction of thickness of theinternal electrode, which enables it to further improve the degree oforientation and polarizability of the crystal grains of thepiezoelectric material.

The internal electrode may also include an inorganic component otherthan the metal included as the major component.

When an inorganic component is included in the internal electrode of themulti-layer piezoelectric element, the inorganic component is preferablythe same as that of the piezoelectric layer, and average particle sizeof the inorganic component is preferably smaller than that of thepiezoelectric layer.

According to the present invention, by including the same inorganiccomponent as that of the piezoelectric particles that constitute thepiezoelectric layer in the internal electrode, and making the averageparticle size of the inorganic component included in the internalelectrode smaller than that of the piezoelectric layer, it is madepossible to increase the effective area of the internal electrode as theparticles of the piezoelectric material that make contact with theinternal electrode become smaller, while suppressing the rigidity of theinternal electrode from increasing due to the addition of the inorganiccomponent, thereby increasing the bonding strength with thepiezoelectric layer and allowing it to apply electric field of higherintensity.

The method of manufacturing the multi-layer electronic component of thepresent invention comprises a process of forming a column-like stack bystacking a plurality of ceramic layers and a plurality of internalelectrodes alternately one on another, a process of trimming thecolumn-like stack to desired dimensions, a process of applying heattreatment to the column-like stack, a process of applying anelectrically conductive paste on the side face of the column-like stack,a process of applying heat treatment to the electrically conductivepaste and form a pair of external electrodes that are connected to theinternal electrode alternately in every other layer, and a process ofapplying a voltage to the external electrodes and carrying outpolarization treatment so that the change in the ratio of latticeconstants c/a becomes 0.5% or less.

In the method of manufacturing the multi-layer electronic component ofthe present invention, it is preferable that the rate of cooling downfrom the maximum temperature of heat treatment is set to t/3 (°C./minute) or less in the process of applying heat treatment to theelectrically conductive paste, where t (° C.) is Curie temperature ofthe ceramic layer.

In the method of manufacturing the multi-layer electronic component ofthe present invention, it is also preferable that the rate of coolingdown in a temperature range from 1.2t to 0.8t in the heat treatment isset to t/3 (° C./minute) or less in the process of applying heattreatment to the electrically conductive paste.

According to the present invention, as described above, the multi-layerelectronic component of high reliability where delamination issuppressed from occurring can be provided.

A second multi-layer piezoelectric element of the present inventioncomprises a stack formed by stacking piezoelectric layers and internalelectrodes alternately, wherein average crystal grain size of a portionof the piezoelectric material that makes contact with the internalelectrode is larger than the average crystal grain size of the otherportion.

A third multi-layer piezoelectric element of the present inventioncomprises a stack formed by stacking piezoelectric layers and internalelectrodes alternately, wherein minimum crystal grain size of a portionof the piezoelectric material that makes contact with the internalelectrode is larger than the minimum crystal grain size of otherportion.

An injection apparatus according to the present invention comprises acontainer that has an injection hole leading to a fuel passage, a pistonthat is housed in the container for opening and closing thecommunication between the fuel passage and the injection hole, and themulti-layer piezoelectric element that is housed in the container anddrives the piston, wherein the multi-layer piezoelectric elementcomprises a stack formed by stacking the piezoelectric layers and theinternal electrodes alternately, while the average crystal grain size ofa portion of the piezoelectric material that makes contact with theinternal electrode is larger than the average crystal grain size of theother portion.

In the second and third multi-layer piezoelectric elements of thepresent invention constituted as described above, by making the averagecrystal grain size or the minimum crystal grain size of a portion of thepiezoelectric material that makes contact with the internal electrode ismade larger than the average crystal grain size or the minimum crystalgrain size of the other portion, it is made possible to distribute theresidual stress cased by difference in thermal expansion between theinternal electrode and the piezoelectric layer uniformly throughout thepiezoelectric particles in the interface of electrodes. This enables itto increase the bonding strength of the internal electrode and thepiezoelectric material in the interface thereof, thereby enabling it tosuppress delamination from occurring and provide a piezoelectricactuator of excellent durability and high reliability where the amountof displacement is suppressed from decreasing during operation.

The multi-layer piezoelectric element of the present invention, sincethe amount of displacement does not substantially change in continuousoperation, enables it to constitute the injection apparatus of excellentdurability and high reliability that includes the multi-layerpiezoelectric element and is capable of operating without failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a multi-layer electronic component according tothe first embodiment of the present invention.

FIG. 2 is a plan view of a ceramic sheet that constitutes themulti-layer electronic component of the first embodiment.

FIG. 3 is an exploded perspective view of a multi-layer green compactthat constitutes the multi-layer electronic component of the firstembodiment.

FIG. 4 is a sectional view of a stacked structure that constitutes themulti-layer electronic component of the first embodiment.

FIG. 5 shows defects formed between a ceramic layer and an internalelectrode of a multi-layer electronic component of the prior art.

FIG. 6A is a perspective view of the constitution of a multi-layerpiezoelectric element according to the second embodiment of the presentinvention.

FIG. 6B is an exploded perspective view of stacked structure ofpiezoelectric layer and internal electrode according to the secondembodiment.

FIG. 7 is a perspective view of a multi-layer capacitor of the priorart.

FIG. 8 is a sectional view showing the constitution of an injectionapparatus of the present invention.

FIG. 9 is a partial sectional view of a multi-layer piezoelectricelement according to the third embodiment of the present invention.

FIG. 10A through 10C show processes for manufacturing the multi-layerpiezoelectric element of the third embodiment.

FIG. 11 is a flow chart showing the sequence of polarization treatmentprocesses according to the third embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a longitudinal sectional view showing the constitution of amulti-layer electronic component (multi-layer piezoelectric actuator)according to the first embodiment of the present invention.

The multi-layer electronic component of the first embodiment has acolumn-like stack 3 of a rectangular prism shape comprising an activesection 8 formed by stacking a plurality of ceramic layers 1 and aplurality of internal electrodes 2 alternately one on another, andinactive sections 9 provided on both ends of the active section 8 in thedirection of stacking, as shown in FIG. 1.

The ceramic layer 1 is made of a piezoelectric ceramic material of whichmain component is lead zirconate titanate Pb(Zr, Ti)O₃ (hereinafterabbreviated as PZT) or barium titanate BaTiO₃, for example, but is notlimited to this composition and may be made of any ceramic material thathas piezoelectric property. The piezoelectric material preferably has ahigh value of piezoelectric strain constant d33.

The thickness of the ceramic layer 1, namely the distance between theinternal electrodes 2, is preferably in a range from 0.05 to 0.25 mm inorder to make the construction smaller and apply high electric field.This is because, while a larger displacement of the multi-layerpiezoelectric element under a given voltage is achieved by stacking alarger number of piezoelectric layers, thick ceramic layers 1 stacked inthe active section 8 make it impossible to make an actuator of smallersize and lower profile when the number of stacked layers is increased,but insulation breakdown may be caused when the ceramic layers 1 stackedin the active section 8 are too thin.

The internal electrodes 2 are formed in a rectangular shape a littlesmaller than the ceramic layer, and are disposed so that one sidethereof is exposed on either one of opposite side faces (externalelectrode forming surface) of the column-like stack every other layer asshown in FIG. 1, while the external electrode 4 is connected on theopposing side faces of the column-like stack 3 whereon one side of theinternal electrode 2 is exposed. As a result, the internal electrodes 2are electrically connected to the external electrodes 4 alternately onevery other layer.

In the multi-layer electronic component of the first embodiment, gapbetween the internal electrode 2 and the ceramic layer 1 of 2 μm or lessis controlled over an area of 50% or more of the interface between theinternal electrode 2 and the ceramic layer 1. In this way it isimportant in the multi-layer electronic component of the firstembodiment, that gap between the internal electrode 2 and the ceramiclayer 1 is controlled to 2 μm or less over an area of 50% or more of theeffectively active region. This enables it to suppress the occurrence ofdelamination, cracks or the like, thereby to achieve high reliability.

When the gap between the internal electrode 2 and the ceramic layer 1 iscontrolled to 2 μm or less over an area of less than 50% of theeffectively active region, cracks may occur in the gap when operatedwith an electric field of high intensity, thus resulting in lowreliability. In order to reduce crack initiating points and improve thereliability, the gap between the internal electrode 2 and the ceramiclayer 1 is more preferably controlled to 2 μm or less over an area of70% or more of the effectively active region.

According to the method of manufacturing the multi-layer electroniccomponent of the present invention, a slurry is prepared by mixing acalcinated powder of piezoelectric ceramics (ceramic powder) such aslead zirconate titanate Pb(Zr, Ti)O₃, an organic binder made of anorganic polymer such as acrylic resin or butyral resin and aplasticizer, and the slurry is formed into a ceramic green sheet 21having thickness of 50 to 250 μm as shown in FIG. 2 by, for example,slip casting method.

According to the present invention, average grain size of calcinatedceramic powder that constitutes the ceramic layer 2 (included in theceramic green sheet 21) is preferably in a range from 0.3 to 0.9 μm. Bycontrolling the average grain size of the calcinated ceramic powder to0.3 μm or larger, it is made possible to reduce the quantity of theorganic binder required to prevent drying crack from occurring whenmaking the ceramic green sheet 21.

By controlling the average grain size of calcinated ceramic powder to0.9 μm or smaller, it is made possible to have the sintering processprogress sufficiently and increase the strength of porcelain, thereby tosuppress the occurrence of cracks due to stress generated by theelectric field, for example, in the multi-layer piezoelectric element.

Thickness of the ceramic green sheet 21 is preferably 90 μm or larger,more preferably 100 μm or larger, in order to ensure a high dielectricbreakdown voltage of the ceramic layer 1 after firing. In order toprevent cracks from occurring in the ceramic green sheet 21 duringhandling, it is preferable to use butyral resin that has high tensilestrength for the organic binder.

Then after punching through the ceramic green sheet 21 intopredetermined dimensions, an electrically conductive paste, thatincludes silver-palladium alloy which makes the internal electrode 2 anda solvent, is applied to one side of the ceramic green sheet 21 to athickness of 1 to 10 μm as shown in FIG. 2 by screen printing process,and is dried to form the internal conductor pattern 22.

The internal conductor pattern 22 has a shape of rectangle having anarea a little smaller than the ceramic green sheet 21 of rectangularshape. One side of the internal conductor pattern 22 is aligned with oneside of the ceramic green sheet 21, while the other side is not.

Then as shown in FIG. 3, a predetermined number of the ceramic greensheets 21 whereon the internal conductor pattern 22 is formed arestacked so that one side of the internal conductor pattern 22 is exposedon one side of the multi-layer green compact 23 in one layer and theopposite side of the internal conductor pattern 22 is exposed on theopposite side of the multi-layer green compact 23 in the next layer, soas to form an active section multi-layer green compact 23 a. Then aninactive section green compact 23 b formed by stacking a plurality ofceramic green sheets 21 without electrically conductive paste printedthereon are stacked on the top and bottom surfaces of the active sectionmulti-layer green compact 23 a, thereby making the multi-layer greencompact 23.

The multi-layer green compact 23 may also be made by, after making thelower inactive section multi-layer green compact 23 b by stacking theplurality of ceramic green sheets 21 without electrically conductivepaste printed thereon, stacking a plurality of ceramic green sheets 21having the internal conductor pattern 22 formed thereon on the lowerinactive section multi-layer green compact 23 b to form the activesection multi-layer green compact 23 a, and stacking a plurality ofceramic green sheets 21 without electrically conductive paste printedthereon on the active section multi-layer green compact 23 a thereby toform the upper inactive section multi-layer green compact 23 b.

There is no limitation to the method of manufacturing the multi-layergreen compact 23, as long as the multi-layer green compact 23 comprisingthe ceramic green sheets 21 and the internal conductor pattern 22 beingstacked one on another is obtained.

The multi-layer green compact 23 is pressurized while being heated so asto integrate the multi-layer green compact 23 and obtain a column-likemulti-layer stack.

Pressure is preferably applied by isostatic pressing in order to ensurehigh precision of stacking, with the pressure preferably in a range from20 to 120 MPa.

The column-like multi-layer stack that has been integrated is cut into apredetermined size and degreased in atmosphere at a temperature from 400to 800° C. for a period of 5 to 40 hours. Then the column-like stack isfired at a temperature from 900 to 1200° C. for a period of 2 to 5hours, so as to obtain the column-like stack 3 as shown in FIG. 4. Thecolumn-like stack 33 has the active section formed by stacking theceramic layers (piezoelectric material layers) 1 and the internalelectrodes 2 alternately, with one side of the internal electrode 2being exposed alternately on the opposing side faces of the stack.

A DC voltage of 0.1 to 3 kV/mm is applied between a pair of externalelectrodes 4 so as to apply polarization treatment to the column-likestack, thereby to complete the multi-layer electronic component as thefinal product. It is important that the change in ratio of latticeconstants c/a after the polarization is not larger than 0.5%. This isbecause the internal electrode 2 may be peeled off the ceramic layer 1due to the stress generated during the polarization treatment when thechange in the ratio c/a is larger than 0.5%. According to the presentinvention, in order to prevent peel-off due to the stress generatedduring the polarization, the change in the ratio c/a is more preferablyless than 0.2%. The ratio of lattice constants c/a is determined bycalculating the lattice constant a from a peak of plane (200) from XRDdiffraction pattern and calculating the lattice constant c similarlyfrom a peak of plane (002).

The manufacturing method described above enables it to control the gapbetween the internal electrode 2 and the ceramic layer 1 to 2 μm orless. When the gap between the internal electrode 2 and the ceramiclayer 1 is larger than 2 μm, such troubles may occur as cracks occur inthe gap when a high voltage is applied or during continuous operationover a long period, thus resulting in low reliability. While theconstitution of the present invention is capable of preventing peel-offfrom occurring in the multi-layer electronic component, a gap largerthan 2 μm may be generated in part of the interface due to mixing offoreign matter in the process. However, satisfactory reliability can bemaintained if the gap is not larger than 2 μm over 50% or more of theactive section.

Then a silver-palladium alloy that includes silver as a main componentis applied to the side face of the column-like stack 3 where the end ofthe internal electrode 2 is exposed as shown in FIG. 1, and such a heattreatment is carried out as the temperature is lowered from the maximumtemperature of heat treatment in a range from 500 to 900° C. at a rateof t/3 (° C./minute) or less where t (° C.) is Curie temperature of theceramic layer 1, thereby to form the external electrode 4. Thus theinternal electrodes 2 are connected to the external electrodes 4 in astaggered manner in every other layer.

A cooling rate faster than t/3 (° C./minute) may lead to stressgenerated in the interface between the internal electrode 2 and theceramic layer 1 due to the difference in thermal expansion between thetwo materials, thus resulting in delamination or cracks.

The cooling rate in a temperature range from 1.2t to 0.8t (° C.) ispreferably t/3 (° C./minute) or lower. The ceramic layer 1 is formed incubic crystal system when the temperature is higher than the Curietemperature, and is formed in rhombohedral crystal system or tetragonalcrystal system when the temperature is lower than the Curie temperature,and therefore delamination is more likely to occur due to the internalstress as the crystal layer changes when the cooling rate is made fasterover the temperature range in which the crystal layer changes.

The gap between the internal electrode 2 and the ceramic layer 1 can bechecked by inspecting a fracture surface by ultrasonic flaw detection orSEM observation. It is preferable to employ the ultrasonic flawdetection technique because it enables it to determine the distributionof gaps throughout the multi-layer electronic component easily withoutdestructing it, although size of the gap can also be determined by SEMobservation of a fracture surface. In case the fracture surface that ispolished to mirror finish is observed with SEM, the internal electrode 2extends into a gap due to the ductility of the internal electrode 2, andtherefore it is important to observe a fracture surface. Based on theobservation of a surface perpendicular to the stacking direction byultrasonic flaw detection, ratio of peel off is determined from theratio of the area where peel-off of 2 μm or larger to the area wherethere is no such large peel-off.

When ultrasonic flaw detection is employed, cross sections of aplurality of layers may be observed at the same time. Sensitivity of theultrasonic flaw detection technique generally becomes lower when thedepth of focus is increased. Therefore, samples that are constitutedfrom a large number of stacked layers and have height of 5 mm or moreare preferably divided by cutting to a height of 2 to 5 mm in adirection perpendicular to the stacking direction, so that each of thedivided portions is subjected to ultrasonic flaw detection to determinethe peel-off ratio. It suffices that portions, where the gap between theinternal electrode 2 and the ceramic layer 1 is not larger than 2 μm,occupy 50% or more of the effectively active region in portions wherefracture can easily initiate due to stress generated by operation,stress generated by electric field and stress generated by buckling,particularly in the vicinity of the top and bottom portions in thestacking direction and at least in a portion near the center.

In the form described above, one column-like stack is made from onemulti-layer green compact 23 as shown in FIG. 3. However, it needs notto say that the present invention can be applied to the manufacture ofthe multi-layer electronic component in which a plurality of internalelectrode patterns are formed on one ceramic green sheet 21, a pluralityof the ceramic green sheets 21 are stacked one on another so as to makethe multi-layer green compact from which a number of column-like stackscan be made, the stacked green compact is cut into pieces ofpredetermined dimensions and make a number of the column-like stacksshown in FIG. 2 at the same time.

For the multi-layer electronic component of the present invention,proportion of cross section of the stacked layer occupied by theinternal electrode 2 is preferably as high as possible in order toprevent the internal electrode 2 and the ceramic layer 1 from peelingoff in the interface thereof. Proportion of the internal electrode 2 ispreferably 70% or more, in particular.

The method of manufacturing the multi-layer electronic component of thepresent invention is preferably used in the manufacture of multi-layerelectronic component such as multi-layer piezoelectric transformer,multi-layer capacitor or multi-layer piezoelectric actuator. The methodof manufacturing the multi-layer electronic component of the presentinvention is particularly preferable for the manufacture of multi-layerpiezoelectric actuator formed from piezoelectric ceramics that iscontinuously operated by applying a high electric field.

Second Embodiment

The multi-layer piezoelectric element according to the second embodimentof the present invention will be described in detail below.

FIG. 6A is a perspective view showing the structure of a multi-layerpiezoelectric element according to the second embodiment. FIG. 6B is anexploded perspective view of the inner structure of the multi-layerpiezoelectric element according to the second embodiment, showing thestacked structure of the piezoelectric layers and the internalelectrodes.

In the multi-layer piezoelectric element according to the secondembodiment, as shown in FIG. 6A, B, external electrodes 15 are connectedso as to establish electrical continuity with the ends of the internalelectrodes 12 that are exposed in every other layer on a pair ofopposing side faces of the stack 13 that is formed by alternatelystacking the piezoelectric layers 11 and the internal electrodes 12 oneon another. Layers on both ends in the stacking direction of the stack13 are the layers formed by stacking a plurality of piezoelectric layers11 without interposing any electrode layer therein, and are calledinactive layers 14 since they are not subjected to voltage and do notexpand or shrink during operation. When the multi-layer piezoelectricelement according to the second embodiment constituted as describedabove is used as a multi-layer piezoelectric actuator, lead wires may besoldered to the external electrodes 15 and connected to an externalvoltage source.

In an active region in which the internal electrodes 12 made of ametallic material such as silver-palladium alloy are disposed betweenthe piezoelectric layers 11, a predetermined voltage is applied to thepiezoelectric layers 11 via the internal electrodes 12, so that thepiezoelectric layers 11 undergo displacement through reversepiezoelectric effect.

The inactive layer 14, in contrast, is constituted from a plurality ofpiezoelectric layers 11 without internal electrode 12 provided therein,and therefore does not undergo displacement even when a voltage isapplied.

The multi-layer piezoelectric element of the second embodiment ischaracterized in that the average crystal grain size of thepiezoelectric layer 11 that faces the internal electrode 12 is largerthan the average crystal grain size of the other portions, so that thecharacteristic effects to be described later can be achieved. The regionof the piezoelectric layer 11 that faces the internal electrode 12herein refers to a region in the vicinity of the interface that is incontact with the internal electrode 12, and includes the region locatednear the periphery of the internal electrode 12.

In the second embodiment, the average crystal grain size of thepiezoelectric layer 11 that faces the internal electrode 12 ispreferably in a range from 1 to 8 μm.

When the average crystal grain size is smaller than 1 μm, the amount ofpiezoelectric displacement decreases due to the size effect, and bendingstrength or the so-called porcelain strength decreases. When minimumcrystal grain size is larger than 8 μm, fracture mode changes fromintergranular fracture to intragranular fracture, thus resulting insmaller bending strength or the so-called porcelain strength.

Also in the second embodiment, the minimum crystal grain size of thepiezoelectric layer 11 that faces the internal electrode 12 may be madelarger than the minimum crystal grain size of the other portions.

Reference is made here to the minimum crystal grain size becauseresidual stress caused by the difference in thermal expansion betweenthe internal electrode 12 and the ceramic layer 11 is concentrated insmall crystal grains among the crystal grains located in the interfaceof the internal electrode 12.

According to the second embodiment, the minimum crystal grain size inthe region that makes contact with the internal electrode 12 ispreferably in a range from 0.5 to 5 μm. When the minimum crystal grainsize is less than 0.5 μm, the amount of piezoelectric displacementbecomes smaller due to the size effect and bending strength or theso-called porcelain strength becomes smaller. When the minimum crystalgrain size is larger than 5 μm, fracture mode changes from intergranularfracture to intragranular fracture, thus resulting in smaller bendingstrength or the so-called porcelain strength.

The average crystal grain size and the minimum crystal grain size can bemeasured by means of SEM (scanning electron microscope). Specifically,the average crystal grain size of the piezoelectric layer 11 that facesthe internal electrode 12 can be measured by drawing a straight lineover the image of the crystal grains of the piezoelectric layer 11 thatfaces the internal electrode 12 captured by the SEM, measuring thelength of line segment enclosed within the boundary of each of randomlyselected 50 crystal grains and averaging the measurements. The presentinvention defines the average crystal grain size in the other portion ofthe piezoelectric layer 11 that faces the internal electrode 12. Theaverage crystal grain size of the other portion is also determinedsimilarly to the above except for drawing a straight line at anarbitrary position in a region other than the piezoelectric layer 11that faces the internal electrode 12.

The minimum crystal grain size is defined as the smallest grain sizeamong the crystal grains shown in the same area of the image where theaverage crystal grain size was measured at the two positions describedabove (the region of the piezoelectric layer that faces the internalelectrode 12 and other region).

In the second embodiment, the average crystal grain size of thepiezoelectric layer 11 that faces the internal electrode 12 is madelarger than the average crystal grain size of the other portions byadjusting the composition of the material such that sintering startingtemperature at which sintering of the internal electrode 12 begins islower than sintering starting temperature at which sintering of thepiezoelectric material 11 begins in the manufacturing process.

Specifically, the electrode pattern is printed with a paste thatincludes a powder of the metal that constitutes the internal electrode12 and oxide of that metal as well, so that a liquid phase can be formedin the interface between the piezoelectric layer 11 and the internalelectrode 12 at a temperature lower than the sintering startingtemperature at which sintering of the piezoelectric material 11 begins.

By controlling the sintering starting temperature at which sintering ofthe internal electrode 12 begins lower than the sintering startingtemperature at which sintering of the piezoelectric material 11 begins;it is made possible that liquid phase is formed first in the internalelectrode 12 so that sintering of the internal electrode 12 proceeds.

In addition, the piezoelectric layer 11 and the internal electrode 12are caused to be sintered in liquid phase as the liquid phase is createdwhen the internal electrode 12 is sintered.

That is, liquid phase is intentionally foisted in the interface of theelectrode and sintering of the piezoelectric porcelain proceeds in aportion that makes contact with the internal electrode 12 so thatportions that have smaller grain size disappear from the interface ofthe electrode with the progress of sintering, thus resulting in growinggrain size in the portion that makes contact with the internal electrode12 and increasing strength of bonding of the interface of the electrode.

According to the manufacturing method described above, the minimumcrystal grain size of piezoelectric layer 11 that faces the internalelectrode 12 can also be made larger than that of the other portions.However, in order to make the minimum crystal grain size of thepiezoelectric layer 11 that faces the internal electrode 12 larger, itis necessary to diffuse the liquid phase, that is formed when sinteringthe electrode, into the piezoelectric material 11. For this reason,temperature is raised to that of sintering the piezoelectric material 11after holding the firing temperature at the liquid phase formingtemperature.

According to the second embodiment, metal composition in the internalelectrode preferably includes group VIII metal and/or group Ib metal asthe main component. Such a metal composition has high heat resistanceand therefore allows it to sinter the piezoelectric material 11 that hasa high sintering temperature and the internal electrode 12 at the sametime.

When the metal composition in the internal electrode 12 includes groupVIII metal and/or group Ib metal as the main component, proportion M1 (%by weight) of group VIII metal and proportion M2 of group Ib metalpreferably satisfy the relations 0<M1≦15, 85≦M2<100 and M1+M2=100.

This is because a proportion of group VIII metal higher than 15% byweight leads to a high specific resistance of the internal electrode 12,resulting in heat generated by the internal electrodes 12 when themulti-layer piezoelectric element is operated continuously. In order toprevent group Ib metal included in the internal electrode 12 fromdiffusing into the piezoelectric material 11, concentration of groupVIII metal is preferably controlled in a range from 0.001% by weight to15% by weight. In view of higher durability of the multi-layerpiezoelectric element, concentration of group VIII metal is preferablyin a range from 0.1% by weight to 10% by weight. When high heatconductivity and extra high durability are required, concentration ofgroup VIII metal is preferably in a range from 0.5% by weight to 9.5% byweight. Moreover, for the maximum durability, concentration of groupVIII metal is preferably in a range from 2% by weight to 8% by weight.

When concentration of group Ib metal is less than 85% by weight, itleads to a high specific resistance of the internal electrode 12,resulting in heat generated by the internal electrodes 12 when themulti-layer piezoelectric element is operated continuously. In order toprevent group Ib metal included in the internal electrode 12 fromdiffusing into the piezoelectric material 11, concentration of group Ibmetal is preferably in a range from 85% by weight to 99.999% by weight.In view of higher durability of the multi-layer piezoelectric element,concentration of group Ib metal is preferably in a range from 90% byweight to 99.9% by weight. When extra high durability is required,concentration of group Ib metal is preferably in a range from 90.5% byweight to 99.5% by weight. Moreover, for the maximum durability,concentration of group Ib metal is preferably in a range from 92% byweight to 98% by weight.

Concentrations by weight of group VIII metal and group Ib metal in themetal composition in the internal electrode 12 can be measured by EPMA(Electron Probe Micro Analysis) or the like.

It is preferable that the group VIII metal included in the metalcomposition in the internal electrode 12 of the present invention is atleast one kind selected from among Ni, Pt, Pd, Rh, Ir, Ru and Os, and Tbmetal is at least one kind selected from among Cu, Ag and Au, becausesuch a composition can be favorably manufactured in mass production bythe alloy powder manufacturing technology currently in practice.

It is more preferable that the group VIII metal included in the metalcomposition in the internal electrode 12 is at least one kind selectedfrom among Pt and Pd, and Ib metal is at least one kind selected fromamong Ag and Au, because such a composition enables it to form theinternal electrode 12 having excellent heat resistance and low specificresistance.

It is further preferable that the group VIII metal included in the metalcomposition in the internal electrode 12 is Ni, because such acomposition enables it to form the internal electrode 12 havingexcellent heat resistance.

It is further preferable that the group Ib metal included in the metalcomposition in the internal electrode 12 is Cu, because such acomposition enables it to form the internal electrode 12 havingexcellent heat conductivity.

Moreover, it is preferable that the internal electrode 12 includes aninorganic compound added to the metal composition. This enables strongbonding between the internal electrode 12 and the piezoelectric material11. The inorganic compound preferably includes a perovskite type oxideconstituted from PbZrO₃—PbTiO₃ as the main component.

In addition, the piezoelectric material 11 preferably includes aperovskite type oxide as the main component. When the piezoelectricmaterial 11 is formed from a perovskite type piezoelectric ceramicmaterial represented by barium titanate (BaTiO₃), for example, highpiezoelectric strain constant d₃₃ that represents the piezoelectriccharacteristic of the material increases the amount of displacement andallows it to sinter the piezoelectric material 11 and the internalelectrode 12 at the same time. The piezoelectric material 11 ispreferably constituted from a material that includes perovskite typeoxide constituted from PbZrO₃—PbTiO₃ that has relatively high value ofhigh piezoelectric strain constant d₃₃ as the main component.

The piezoelectric material 11 is preferably sintered at a temperature ina range from 900 to 1000° C. This is because the material cannot befully sintered at a temperature below 900° C., thus making it difficultto make the piezoelectric material 11 with high density. When thesintering temperature is higher than 1000° C., on the other hand, largestress is generated due to the difference in shrinkage between theinternal electrode 12 and the piezoelectric material 11 when fired, thusresulting in cracks generated during continuous operation of themulti-layer piezoelectric element.

Change in the composition of the internal electrode 12 caused by firingis preferably not more than 5%. When the change in the composition ofthe internal electrode 12 caused by firing exceeds 5%, much metalcomposition in the internal electrode diffuses into the piezoelectricmaterial 11 thus making it impossible for the internal electrode 12 toaccommodate the contraction and expansion of the multi-layerpiezoelectric element during operation.

Change in the composition of the internal electrode 12 refers to achange in the composition of the internal electrode 12 caused byevaporation of the metal composition that constitutes the internalelectrode 12 during firing or diffusion thereof into the piezoelectricmaterial 11.

In the multi-layer piezoelectric element of the second embodiment, oneend of the internal electrode is exposed on the side face of the stackalternately at every other layer while the other end of the internalelectrode is located inside from one side face. It is preferable that agroove is formed toward the end that is located inside and the groove isfilled with a dielectric material of which Young's modulus is lower thanthat of the piezoelectric material. This constitution enables it tomitigate the stress generated by the displacement of the multi-layerpiezoelectric element during operation, so that heat generation from theinternal electrode 12 can be suppressed during continuous operation.

Now the method for manufacturing the multi-layer piezoelectric elementof the present invention will be described.

Calcinated powder of piezoelectric ceramic material constituted fromperovskite type oxide such as PbZrO₃—PbTiO₃, a binder made of an organicpolymer such as acrylic resin or butyral resin and a plasticizer such asDBP (dibutyl phthalate) or DOP (dioctyl phthalate) are mixed to form aslurry which is formed into a ceramic green sheet that would become thepiezoelectric material 11 by a known method such as doctor blade processor tape molding method such as calender roll process.

Then a metal oxide such as silver oxide, a binder and a plasticizer aremixed with the metal composition that constitutes the internal electrode12 such as silver-palladium alloy to prepare an electrically conductivepaste which is applied onto the top surface of the ceramic green sheetby screen printing or the like to a thickness of 1 to 40 μm.

A plurality of the green sheets having the electrically conductive pasteprinted thereon are stacked one on another, with the stack being heatedat a predetermined temperature to remove the binder and fired at atemperature in a range from 900 to 1200° C. thereby to make the stack13.

At this time, a dense stack can be made by adding metal powder thatconstitutes the internal electrode such as silver-palladium alloy in thegreen sheet in the portion of the inactive layer 14, or printing aslurry consisting of the metal powder that constitutes in the internalelectrode such as silver-palladium alloy, an inorganic compound, abinder and a plasticizer onto the green sheets, which enables it tomatch the inactive layer 14 and the other portions in the behavior ofshrinking and the shrinking ratio during the sintering process.

The method of making the stack 13 is not limited to that describedabove, and any manufacturing method may be employed as long as the stack13 can be made in such a constitution as a plurality of thepiezoelectric layers 11 and a plurality of the internal electrodes 12are stacked alternately one on another.

Then the internal electrode 12 of which one end is exposed on the sideface of the multi-layer piezoelectric element and the internal electrode12 of which one end is not exposed are formed alternately, and a grooveis formed in the portion of the piezoelectric material located betweenthe internal electrode 12 of which one end is not exposed and theexternal electrodes 15, with the groove being filled with a dielectricmaterial such as resin or rubber of which Young's modulus is lower thanthat of the piezoelectric material 11. The groove is formed on the sideface of the stack 13 by means of a dicing apparatus or the like.

The electrically conductive material that constitutes the externalelectrode 15 is preferably silver or an alloy based on silver that has alow value of Young's modulus, so as to absorb the stress generated bythe contraction and expansion of the actuator.

The external electrode 15 may be formed as follows. An electricallyconductive silver-glass paste is prepared by adding a binder to a glasspowder and formed into a sheet that is dried to remove solvent whilecontrolling the density of the sheet in a range from 6 to 9 g/cm³. Thesheet is transferred onto the external electrode forming surface of thecolumn-like stack 13, and is baked at a temperature that is higher thanthe softening point of the glass and is not higher than the meltingpoint (965° C.) of silver and is ⅘ of the firing temperature (° C.) orlower. In this process, the binder included in the sheet formed from theelectrically conductive silver-glass paste is removed and the externalelectrode 15 is formed from a porous electrical conductor having3-dimensional mesh structure.

The temperature at which the electrically conductive silver-glass pasteis baked is preferably in a range from 550 to 700° C. for the purpose ofeffectively forming a neck, joining silver that is included in theelectrically conductive silver-glass paste and the internal electrode 12through diffusion, effectively causing the voids in the externalelectrode 15 to remain and partially joining the external electrode 15and the side face of the column-like stack 13. Softening point of theglass component included in the electrically conductive silver-glasspaste is preferably in a range from 500 to 700° C.

When the baking temperature is higher than 700° C., sintering of thesilver powder of the electrically conductive silver-glass paste proceedsexcessively, such that the porous electrical conductor of 3-dimensionalmesh structure cannot be effectively formed. That is, the externalelectrode 15 becomes too dense, resulting in Young's modulus of theexternal electrode 15 that is too high to effectively absorb the stressgenerated during operation, eventually leading to breakage of theexternal electrode 15. Baking is preferably carried out at a temperaturethat is not higher than 1.2 times the softening point of the glass.

When the baking temperature is lower than 550° C., end of the internalelectrode 12 and the external electrode 15 cannot be joined sufficientlythrough diffusion, and therefore the neck cannot be formed thusresulting in spark occurring between the internal electrode 12 and theexternal electrode 15 during operation.

Thickness of the sheet formed from the electrically conductivesilver-glass paste is preferably smaller than the thickness of thepiezoelectric layer 11. More preferably, the thickness is 50 μm or lessin order to accommodate the contraction and expansion of the actuator.

Then the stack 13 in which the external electrode 15 is formed isimmersed in a silicone rubber solution while deaerating the siliconerubber solution by evacuation, so as to fill the groove of the stack 13with the silicone rubber. The stack 13 is pulled out of the siliconerubber solution and is coated with the silicone rubber on the side facesthereof. Then the silicon rubber that fills the groove and covers theside faces of the column-like stack 13 is hardened thereby completingthe multi-layer piezoelectric element of the present invention.

Lead wires are connected to the external electrodes 15, a DC voltage of0.1 to 3 kV/mm is applied between the pair of external electrodes 15 viathe lead wires so as to apply polarization treatment to the stack 13,thereby to complete the multi-layer piezoelectric actuator comprisingthe multi-layer piezoelectric element of the present invention. When thelead wires are connected to an external voltage source and the voltageis supplied via the lead wires and the external electrodes 15 to theinternal electrodes 12, the piezoelectric layers 11 of the multi-layerpiezoelectric element of the present invention undergoes a significantamount of displacement by the reverse piezoelectric effect, so as todrive, for example, an automobile fuel injection valve that suppliesfuel to the engine.

An electrical conductivity assisting member made of an electricallyconductive adhesive with a metal mesh or a mesh-like metal sheetembedded therein may be formed on the external surface of the externalelectrode 15. In this case, the electrical conductivity assisting memberprovided on the external surface of the external electrode 15 allows itto supply a large electric current to the actuator, thereby enabling itto draw a large current through the electrical conductivity assistingmember even when operated at a high speed, thus reducing the currentflowing in the external electrode 15. This makes it possible to preventthe external electrodes 15 from breaking due to localized heatgeneration, thus resulting in greatly improved reliability. Moreover,because the metal mesh or the mesh-like metal sheet is embedded in theelectrically conductive adhesive, cracks can be prevented from occurringin the electrically conductive adhesive.

The metal mesh refers to a structure of entwined metal wires, and themesh-like metal sheet refers to a metal sheet with a number of holespunched therethrough.

It is also preferable that the electrically conductive adhesive thatconstitutes the electrical conductivity assisting member is formed frompolyimide resin including silver powder dispersed therein. By dispersingthe silver powder that has low specific resistance in the polyimideresin that has high heat resistance, the electrical conductivityassisting member can maintain low resistivity and high bonding strengtheven when used at high temperatures. More preferably, the electricallyconductive particles are non-spherical particles such as flakes oracicular particles. When the electrically conductive particles arenon-spherical particles such as flakes or acicular particles, theelectrically conductive particles can be firmly entwined with eachother, thereby increasing the shear strength of the electricallyconductive adhesive.

The multi-layer piezoelectric element of the present invention is notlimited to the constitution of the second embodiment described above,and various modifications can be made to an extent that does not deviatefrom the scope of the present invention.

While an example where the external electrodes 15 are formed on theopposing side faces of the stack 13 has been described above, a pair ofexternal electrodes may be formed on, for example, adjacent side facesaccording to the present invention.

FIG. 8 shows the injection apparatus according to the present invention,where an injection hole 33 is provided on one end of a container 31 anda needle valve 35 that can open and close the injection hole 33 ishoused in the container 31.

A fuel passage 37 is provided so as to be capable of communicating withthe injection hole 33, and is connected to a fuel source that isprovided outside of the apparatus, so as to supply the fuel through thefuel passage 37 at a high pressure that is maintained constant. When theneedle valve 35 opens the injection hole 33, the fuel supplied to thefuel passage 37 is injected into a fuel chamber (not shown) of aninternal combustion engine at a high pressure that is maintainedconstant.

Diameter of the needle valve 35 is made larger at the top end to becomea piston 41 that is movable while sliding in a cylinder 39 formed in thecontainer 31. The piezoelectric actuator 43 is housed in the container31.

In the injection apparatus having the constitution described above, whenthe piezoelectric actuator 43 expands under a voltage applied thereto,the piston 41 is pressed so that the needle valve 35 closes theinjection hole 33 thereby stopping the fuel supply. When application ofthe voltage is stopped, piezoelectric actuator 43 contracts and abelleville spring pushes back the piston 41 so that the injection hole33 communicates with the fuel passage 37 and the fuel is injected.

While FIG. 8 relates to the multi-layer piezoelectric element and theinjection apparatus, the present invention is not limited to theconstitution shown in FIG. 8. For example, the present invention can beapplied to a fuel injection apparatus of automobile engine, liquidejecting apparatus of ink jet printer or the like or a drive unit usedin precision positioning device or vibration preventing device for anoptical apparatus, or to sensor devices such as a sensor element mountedin combustion pressure sensor, knocking sensor, acceleration sensor,load sensor, ultrasonic sensor, pressure sensor, yaw rate sensor or thelike, or used as a circuit component mounted in piezoelectric gyro,piezoelectric switch, piezoelectric transformer, piezoelectric breakeror the like, and is also applicable to other purposes, as long as thepiezoelectric characteristic is utilized.

Third Embodiment

The piezoelectric electronic component according to the third embodimentof the present invention is a multi-layer piezoelectric actuator ofsimilar constitution as that of the first embodiment, with a part of themanufacturing process different from that of the first embodiment.

FIG. 9 is an enlarged sectional view of a part of the multi-layerpiezoelectric actuator of the third embodiment, with similar componentsidentified with similar reference numerals as in the first embodiment.

Thickness of the piezoelectric layer 1, namely the distance between theinternal electrodes 2, is preferably not larger than 200 μm, or morepreferably not larger than 150 μm, in order to make the constructionsmaller and apply high electric field. On the other hand, thickness ofthe piezoelectric layer 1 is set not smaller than 50 μm, preferably notsmaller than 70 μm, in order to reduce the transient time of applying avoltage to the piezoelectric layer 1 and enable faster response. Thusthe number of stacked layers is preferably 200 or more. While largerdisplacement of the multi-layer piezoelectric element under a givenvoltage is achieved by stacking a larger number of piezoelectric layers,stacking a larger number of thick piezoelectric layers 1 in themulti-layer piezoelectric body 3 makes it impossible to make an actuatorof smaller size and lower profile. On the other hand, insulationbreakdown may be caused when thickness of the piezoelectric layers 1 inthe multi-layer piezoelectric body 3 is too small. Therefore, thethickness is preferably in the range described above.

Average crystal grain size of crystal grains that constitute thepiezoelectric material according to the third embodiment is preferably 5μm or less, and more preferably 3 μm or less.

In the multi-layer piezoelectric element of the first embodiment, it isimportant that change in the degree of orientation f of the crystalgrains of the piezoelectric material is controlled to within 5% afteroperation, by employing the manufacturing method described below. Inorder to enable continuous operation of more than 10⁹ cycles, degree oforientation f is preferably controlled to within 3%. An injectionapparatus of high reliability can be made by employing the multi-layerpiezoelectric element that is capable of repetitive operations of morethan 10⁹ cycles under such conditions as load of 150 kgf, temperature of150° C. and frequency of 50 Hz.

When change in the degree of orientation f of the crystal grains of thepiezoelectric material exceeds 5% after operation, constantpiezoelectric characteristic cannot be obtained during continuousoperation and, moreover, service life becomes shorter.

FIG. 10 is a flow chart showing the sequence of processes to manufacturethe multi-layer piezoelectric element of the present invention. Themanufacturing method will now be described below taking a multi-layerpiezoelectric actuator as a representative example of the multi-layerpiezoelectric element of the third embodiment.

In the manufacturing method for the multi-layer piezoelectric element ofthe third embodiment, for example, a ceramic green sheet 21 havingthickness in a range from 50 to 250 μm is made similarly to the firstembodiment (FIG. 10A).

In the manufacturing method according to the third embodiment,preferable range of the average particle size of the piezoelectricpowder that is calcinated powder that makes the piezoelectric layer 1and preferable range of thickness of the green sheet 21 are similar tothose of the first embodiment.

A conductor pattern 22 is formed on one side of the green sheet 21 thathas been punched through to predetermined dimensions similarly to thefirst embodiment. In this case, it is preferable to mix a ceramic powderin the electrically conductive paste similarly to the second embodiment.

Then a multi-layer piezoelectric green compact 23 is made similarly tothe first embodiment and is cut into predetermined dimensions, beforebeing degreased in air atmosphere and fired so as to make themulti-layer piezoelectric stack 3.

In the third embodiment, firing is carried out preferably at atemperature not higher than 1000° C., especially at 980° C. or lower inorder to increase the proportion of Ag in the internal electrode 2 andreduce the manufacturing cost.

Then similarly to the first embodiment, the external electrode pastethat includes Ag-glass is applied to the end face of the piezoelectricstack 3, and is heated at a temperature in a range from 500° C. to 900°C., so as to form the external electrode 4 shown in FIG. 10. In thiscase, cooling rate from the maximum temperature of heat treatment ispreferably in the same range as that of the first embodiment.

The multi-layer piezoelectric element made as described above issubjected to polarization treatment according to the procedure shown inFIG. 11.

Specifically, the multi-layer piezoelectric element is immersed in anoil bath that is heated to a temperature from 100° C. to 400° C., and aDC voltage of 0.1 to 3 kV/mm is applied between a pair of the externalelectrodes 4 that are formed on the device so as to fully polarize thecrystal grains that constitute the piezoelectric layer.

After the polarization treatment, the device is cooled down to roomtemperature below Curie temperature while maintaining the appliedvoltage. Then after cooling down to the room temperature, electric fieldis reduced. With this polarization treatment, the multi-layerpiezoelectric element of the third embodiment is completed.

It is important to apply the polarization treatment to the multi-layerpiezoelectric element of the third embodiment in the procedure describedabove.

When the internal electrode 2 includes Ag, for example, Ag normallydiffuses toward the piezoelectric layer during firing. When Ag diffuses,oxygen defects are formed in the porcelain due to mutual diffusion withthe porcelain of the piezoelectric layer. The oxygen defects becomeoxygen hole ions during continuous operation, affecting the movingdirection of ions at B site (Zr, Ti) constituting the piezoelectriclayer, so that the preferred orientation of the porcelain changes withtime. According to the present invention, in contrast, sufficientpolarization is carried out under the conditions described above, andtherefore the change in preferred orientation of the porcelain with timeis suppressed.

According to the third embodiment, the rate of cooling down after thepolarization treatment is preferably set to t/3 (° C./minute) or less,where t (° C.) is Curie temperature of the piezoelectric layer. Such acooling rate enables it to more effectively suppress the piezoelectriccharacteristic from changing after operation.

The change in the ratio of lattice constants c/a of the piezoelectricmaterial that constitutes the piezoelectric layer after polarization ispreferably 0.5% or less. This is because, when the change in c/a islarger than 0.5%, stress generated during polarization causes peel-offbetween the internal electrode 2 and the piezoelectric layer 1. In thethird embodiment, in order to effectively prevent peel-off due topolarization from occurring, change in c/a is more preferably 0.2% orless. The ratio of lattice constants c/a is determined by calculatingthe lattice constant a from a peak of plane (200) from XRD diffractionpattern and calculating the lattice constant c from a peak of plane(002).

In the third embodiment, it is made possible to control the change inthe preferred orientation of the crystal grains that constitutes thepiezoelectric layer 1 after operation to within 5% by employing themanufacturing method described above.

The method of manufacturing the multi-layer electronic component of thethird embodiment is preferably used in the manufacture of multi-layerelectronic component such as multi-layer piezoelectric transformer,multi-layer capacitor or multi-layer piezoelectric actuator. The methodof manufacturing the multi-layer electronic component of the presentinvention is particularly preferable or the manufacture of multi-layerpiezoelectric actuator formed from piezoelectric ceramics that iscontinuously operated by applying high electric field. Operation test ispreferably carried out by conducting repetitive operations of more than10⁹ cycles under such conditions as load of 150 kgf, temperature of 150°C. and frequency of 50 Hz.

An injection apparatus similar to that described in the secondembodiment can be made by using the multi-layer piezoelectric element ofthe third embodiment that has the constitution described above.

While the third embodiment has been described by way of an example wherethe internal electrode 2 is made of Ag—Pd, the present invention is notlimited to this constitution and the internal electrode 2 may be formedby using various materials.

However, the metal composition that constitutes the internal electrode 2preferably consists of either the group VIII metal or the group Ibmetal, or both the group VIII metal and the group Ib metal as the maincomponent. Particularly, proportion M1 (% by weight) of the group VIIImetal and proportion M2 of the group Ib metal preferably satisfy therelations 0.001≦M1≦15, 85≦M2≦99.999 and M1+M2=100, more preferably3≦M1≦8 and 92≦M2≦97.

It is preferable that the group VIII metal is at least one kind selectedfrom among Ni, Pt, Pd, Rh, Ir, Ru and Os, and the group Ib metal is atleast one kind selected from among Cu, Ag and Au. It is more preferablethat the group VIII metal is at least one kind selected from among Ptand Pd, and the group Ib metal is at least one kind selected from amongAg and Au. It is furthermore preferable that the group VIII metal is Ni,the group Ib metal is Cu.

Thickness of the internal electrode of the present invention ispreferably 5 μm or less, and more preferably 4 μm or less.

The internal electrode 2 of the present invention includes an inorganiccomponent, and the inorganic component is preferably the same as that ofthe piezoelectric layer 1 and has average particle size smaller thanthat of the piezoelectric layer 1.

Example 1

In Example 1, the multi-layer electronic component of the firstembodiment shown in FIG. 1 was made and was evaluated for the size ofthe gap between the internal electrode and the ceramic layer.

First, a slurry was prepared by mixing a calcinated powder ofpiezoelectric ceramics such as lead zirconate titanate Pb(Zr, Ti)O₃having Curie temperature of 300° C. and particle size of 0.7 μm, anorganic binder made of butyral resin and a plasticizer, and the slurrywas formed into a ceramic green sheet 21 having thickness of 150 μm byslip casting method.

Then an electrically conductive paste, that includes silver-palladiumalloy which makes the internal electrode 2 and a solvent, is applied toone side of the ceramic green sheet 21 to a thickness of 4 μm as shownin FIG. 2 by screen printing process, so as to form the internalconductor pattern 22.

Then 30 pieces of the ceramic green sheets 21 whereon the internalconductor pattern 22 was formed were stacked. Then 5 pieces of theceramic green sheet 21 without electrically conductive paste printedthereon were stacked on the top and bottom surfaces of the stack,thereby making the multi-layer green compact 23 having the constructionshown in FIG. 3.

The multi-layer green compact 23 was put into a die and was heated to90° C. while applying pressure of 100 MPa by means of an isostatic pressso as to be integrated.

The multi-layer green compact 23 that was integrated was cut into 10 mmsquare and was heated to 800° C. for 10 hours to remove the binder,followed by firing at 1130° C. for 2 hours, thereby to obtain thecolumn-like stack 3.

Ag-glass paste including Ag as the main component was applied to a pairof opposing side faces of the active section and was heated at 750° C.for 1 hour before being cooled down at the rate shown in Table 1 therebyto form the external electrode 4.

Then a DC voltage of 3 kV/mm was applied between the positive andnegative external electrodes 4 so as to apply polarization treatment for15 minutes, thereby to make the multi-layer piezoelectric element. Thechange in ratio of lattice constants c/a after the polarization is shownin Table 1.

TABLE 1 Proportion of area with Change Gap in distance Cooling rate inc/a interface 2 μm No (° C./minute) (%) μm or less % Delamination *1-1 150 Curie 0.60 2.8 5 Occurred temperature/2 1-2 100 Curie 0.45 1.6 52 Notemperature/3 1-3  50 Curie 0.20 1.0 71 No temperature/6 1-4  10 Curie0.05 0.3 86 No temperature/30 1-5  5 Curie 0.05 0.3 98 No temperature/60

As shown in Table 1, samples Nos. 1-2 through 1-5 within the scope ofthe present invention showed no delamination in the interface, as theinternal electrode and the piezoelectric layer are located near to eachother with distance not larger than 2 μm in 50% or more of the activeregion where two adjacent internal electrodes oppose each other. Insample No. 1-1 that was made by cooling down at a rate out of the scopeof the present invention, in contrast, since the gap is as large as 2.8μm in the interface and the proportion of area where the gap is 2 μm orless is only 5% due to the fast cooling rate, occurrence of delaminationwas confirmed by observation of the appearance with a binocularmicroscope.

Example 2

In Example 2, the multi-layer piezoelectric actuator of the secondembodiment was made and was evaluated as described below.

First, a slurry was prepared by mixing a calcinated powder ofpiezoelectric ceramics including lead zirconate titanate (PbZrO₃—PbTiO₃)having average particle size of 0.4 μm as the main component, a binderand a plasticizer, and the slurry was formed into a ceramic green sheetthat would become the piezoelectric layer 11 having thickness of 150 μmby doctor blade method.

Then an electrically conductive paste was applied to one side of theceramic green sheet to a thickness of 3 μm by screen printing process.Then 300 pieces of the ceramic green sheets were stacked and fired at1000° C. after hold the temperature at 800° C. The electricallyconductive paste was made by adding silver oxide and a binder to thesilver-palladium alloy, and the proportion of the silver-palladium alloycan be determined arbitrarily.

After firing, a groove measuring 50 μm in depth and 50 μm in width wasformed at the end of the internal electrode located on the side face ofthe stack in every other layer, by means of a dicing apparatus.

Then 90% by volume of silver powder of flake-like particle shape havingaverage particle size of 2 μm and 10% by volume of amorphous glasspowder having softening point of 640° C. including silicon as the maincomponent having average particle size of 2 μm were mixed, and 8 partsby weight of a binder is added for 100 parts by weight in total of thesilver powder and the glass powder, so as to prepare the electricallyconductive silver-glass paste by fully mixing the powders. Theelectrically conductive silver-glass paste thus prepared was screenprinted onto a release film. After drying, the paste film was peeled offthe release film to obtain a sheet of electrically conductivesilver-glass paste. Density of the green sheet as measured by Archimedesmethod was 6.5 g/cm³.

The sheet of the electrically conductive silver-glass paste wastransferred onto the surface of the external electrode 15 of the stack13, and was baked at 650° C. for 30 minutes so as to form the externalelectrode 15 made of a porous electrically conductive material having3-dimensional mesh structure. Void ratio of the external electrode 15measured by analyzing a photograph of a cross section of the externalelectrode 15 with an image analyzer was 40%.

Lead wires were connected to the external electrodes 15, and a DCelectric field of 3 kV/mm was applied via the lead wires between thepositive and negative external electrodes 15 so as to apply polarizationtreatment for 15 minutes, thereby to make the multi-layer piezoelectricactuator comprising the multi-layer piezoelectric element shown in FIG.1.

When a DC voltage of 170 V was applied across the multi-layerpiezoelectric element obtained as described above, the multi-layerpiezoelectric element underwent displacement of 45 μm in the stackingdirection. The multi-layer piezoelectric element was then subjected toan AC voltage varying between 0 V and +170 V at frequency of 150 Hz foroperation test at the room temperature.

The multi-layer piezoelectric element shown in Tables 2 and 3 that wereoperated for 1×10⁹ cycles were cut into pieces measuring 3 mm×4 mm×36mm, that were tested for bending strength by 4-point bending testaccording to JIS R1601. When the electrode surface of the internalelectrode 12 was disposed substantially at right angles to thelongitudinal direction of the test piece, all test pieces fractured inthe interface between the internal electrode 12 and the piezoelectriclayer 11.

The samples shown in Table 2 were observed with SEM to measure theaverage crystal grain size of the piezoelectric layer 11 in a portionmaking contact with the internal electrode 12 and the average crystalgrain size of other portion, so as to investigate the relationshipbetween the average crystal grain size and the bending strength.Specifically, the average crystal grain size was measured by drawing astraight line over the image of the piezoelectric grains that face theinternal electrode captured by the SEM, measuring the length of linesegment enclosed within the boundary of each of randomly selected 50crystal grains and averaging the measurements.

The average crystal grain size in the other portion was determined bydrawing a straight line at an arbitrary position of the image in aregion other than the piezoelectric layer that faces the internalelectrode and measuring the length of line segment enclosed within theboundary of each of randomly selected 50 crystal grains and averagingthe measurements.

The minimum crystal grain size is defined as the smallest grain sizeamong the crystal grains shown in the same area of the image where theaverage crystal grain size was measured.

For the purpose of comparison, relationship between the average crystalgrain size and the bending strength was also investigated when averagecrystal grain size of the piezoelectric layer 11 of a portion makingcontact with the internal electrode 12 was made the same as or largerthan the average crystal grain size of other portion by the conventionalmanufacturing method.

The samples shown in Table 3 were observed with SEM to measure theminimum crystal grain size and the maximum crystal grain size of thepiezoelectric layer 11 of a portion that makes contact with the internalelectrode 12, and the minimum crystal grain size and the maximum crystalgrain size of the other portion, so as to investigate the relationshipbetween these values and the bending strength. The measuring method wassimilar to that shown in Table 2. For the purpose of comparison,relationship between the minimum crystal grain size and the maximumcrystal grain size and the bending strength was also investigated whenthe minimum crystal grain size and the maximum crystal grain size of thepiezoelectric layer 11 of a portion making contact with the internalelectrode 12 were made substantially the same as or larger than theminimum crystal grain size and the maximum crystal grain size of theother portion. The results are shown in Tables 2 and 3.

TABLE 2 Average crystal Bending Average crystal grain strength No grainsize 1 (μm) size 2 (μm) (MPa) *2-1  0.4 0.4 34.3 2-2 1.0 0.8 84.6 2-31.9 1.7 90.2 2-4 2.7 2.4 92.4 2-5 3.8 3.5 103.6 2-6 5.7 5.2 99.6 2-7 8.07.9 83.0 *2-8  9.2 9.8 40.2

The average crystal grain size 1 shown in Table 2 represents the averagecrystal grain size (μm) of the piezoelectric layer in the vicinity ofthe internal electrode, and the average crystal grain size 2 representsthe average crystal grain size (μm) of the piezoelectric layer in aportion other than the vicinity of the internal electrode.

TABLE 3 Maximum Minimum Maximum Minimum crystal crystal crystal crystalBending grain size grain size grain size grain size strength No 1 (μm) 1(μm) 2 (μm) 2 (μm) MPa *2-9  1.2 0.1 1.3 0.2 34.3 2-10 2.4 0.5 2.3 0.384.6 2-11 2.6 1.0 2.8 0.3 90.2 2-12 3.1 2.7 3.0 0.3 92.4 2-13 4.5 3.84.6 0.3 103.6 2-14 6.2 5.0 6.8 0.2 99.6 2-15 8.4 4.6 8.1 0.4 83.0 *2-16 10.1 5.0 11.2 5.2 40.2

The maximum crystal grain size 1 shown in Table 3 represents the maximumcrystal grain size (μm) of the piezoelectric layer in the vicinity ofthe internal electrode, and the minimum crystal grain size 1 representsthe minimum crystal grain size (μm) of the piezoelectric layer in thevicinity of the internal electrode.

The maximum crystal grain size 2 shown in Table 3 represents the maximumcrystal grain size (μm) of the piezoelectric layer in a portion otherthan the vicinity of the internal electrode, and the minimum crystalgrain size 2 represents the minimum crystal grain size (μm) of thepiezoelectric layer in a portion other than the vicinity of the internalelectrode.

From Table 2, it can be seen that sufficient bending strength cannot beobtained when the average crystal grain size of the piezoelectric layer11 of a portion facing the internal electrode 12 is smaller than or thesame as the average crystal grain size of the other portion (samplesNos. 2-1, 2-8), while bending strength can be improved when the averagecrystal grain size of the piezoelectric layer 11 of a portion facing theinternal electrode 12 is larger than the average crystal grain size ofthe other portion (samples Nos. 2-2 through 2-7).

From Table 3, it can be seen that the maximum crystal grain size of thepiezoelectric layer 11 of a portion facing the internal electrode 12 isthe same as or larger than the maximum crystal grain size of the otherportion. However, when the minimum crystal grain size is compared, itcan be seen that sufficient bending strength cannot be obtained when theminimum crystal grain size of the piezoelectric layer 11 of a portionfacing the internal electrode 12 was smaller than minimum crystal grainsize of the other portion (samples Nos. 2-9, 2-16), while bendingstrength can be improved when the minimum crystal grain size of thepiezoelectric layer 11 of a portion facing the internal electrode 12 islarger than the minimum crystal grain size of the other portion (samplesNos. 2-10 through 2-14).

From Table 3, it can also be seen that bending strength can be improvedby setting the minimum crystal grain size of the piezoelectric layer 11facing the internal electrode 12 in a range from 0.5 to 5 μm.

In any case, since all test pieces fractured in the interface betweenthe internal electrode 12 and the piezoelectric layer 11, it can be seenthat bonding strength in the interface between the internal electrode 12and the piezoelectric layer 11 can be improved by making the crystalgrain size (average crystal grain size, minimum crystal grain size) ofthe piezoelectric layer 11 of a portion facing the internal electrode 12larger than the crystal grain size (average crystal grain size, minimumcrystal grain size) of the other portion.

Example 3

As Example 3 related to the second embodiment, multi-layer piezoelectricelements having different compositions of the internal electrode 12 weremade and evaluated for the relation with the bending strength bymeasuring the minimum crystal grain size and the maximum crystal grainsize of the piezoelectric layer making contact with the electrode, andmeasuring the minimum crystal grain size and the maximum crystal grainsize of the other portion under the same conditions as those of Example2. The results are shown in Table 4. Change in the amount ofdisplacement was also measured on each test piece. Change in the amountof displacement is the decrease in displacement of the multi-layerpiezoelectric element determined by comparing the displacement (μm) ofthe multi-layer piezoelectric element after undergoing 1×10⁹ cycles ofoperation and the initial displacement (μm) of the multi-layerpiezoelectric element before the continuous operation. The results arealso shown in Table 4.

TABLE 4 Content of other metals in internal Pd content Pt content Agcontent electrode No (% by weight) (% by weight) (% by weight) (% byweight) 3-17 0 0 100 0 3-18 0.001 0 99.999 0 3-19 0.01 0 99.99 0 3-200.1 0 99.9 0 3-21 0.5 0 99.5 0 3-22 1 0 99 0 3-23 2 0 98 0 3-24 4 1 95 03-25 5 0 95 0 3-26 8 0 92 0 3-27 9 0 91 0 3-28 9.5 0 90.5 0 3-29 10 0 900 3-30 15 0 85 0 3-31 20 0 80 0 3-32 30 0 70 0 3-33 0 0 0 Cu 100% 3-340.1 0 0 Cu 99.9% 3-35 0 0 0 Ni 100% Average Average Bending grain sizegrain size Change in strength No 1 (μm) 2 (μm) displacement (%) (MPa)3-17 Fractured due to migration — during operation. 3-18 4.2 3.5 0.796.8 3-19 4.2 3.6 0.7 97.1 3-20 4.1 3.6 0.4 98.0 3-21 4.0 3.6 0.2 99.83-22 4.0 3.6 0.2 100.4 3-23 3.9 3.6 0 102.5 3-24 3.8 3.5 0 105.1 3-253.8 3.5 0 107.2 3-26 3.7 3.4 0 104.2 3-27 3.6 3.4 0.2 100.7 3-28 3.5 3.30.2 99.2 3-29 3.4 3.3 0.4 98.2 3-30 3.3 3.2 0.7 97.2 3-31 2.7 2.5 0.990.5 3-32 2.5 2.3 0.9 90.3 3-33 3.8 3.5 0.2 102.1 3-34 3.8 3.5 0 103.13-35 3.7 3.4 0.4 100.9

The average crystal grain size 1 shown in Table 4 represents the averagegrain size (μm) of the piezoelectric layer in the vicinity of theinternal electrode, and the average crystal grain size 2 represents theaverage grain size (μm) of the piezoelectric layer in a portion otherthan the vicinity of the internal electrode.

Change in the amount of displacement shown in Table 4 is the differencebetween the initial displacement and the displacement after continuousoperation test.

Table 4 shows that continuous operation became impossible as themulti-layer piezoelectric element broke due to silver migration, whenthe internal electrode 12 was made of 100% silver in sample No. 3-17. Insamples other than No. 3-17, the average grain size of the piezoelectriclayer 11 facing the internal electrode 12 was larger than the averagecrystal grain size of the piezoelectric layer 11 in the other portion.In samples Nos. 3-31 and 3-32, the content of the group VIII metal washigher than 15% by weight and the content of the group Ib metal was lessthan 85% by weight in the metal composition in the internal electrode12, and therefore the multi-layer piezoelectric element deterioratesthrough continuous operation and durability of the multi-layerpiezoelectric actuator decreases. Thus bending strength decreases inthis case.

In samples Nos. 3-18 through 3-30 and 33 through 35, where the averagegrain size of the piezoelectric layer 11 facing the internal electrode12 was larger than the average crystal grain size of the piezoelectriclayer 11 in the other portion, and proportion M1 (% by weight) of thegroup VIII metal and proportion M2 of the group Ib metal in metalcomposition in the internal electrode preferably satisfy the relations0≦M1≦15, 85≦M2≦100 and M1+M2=100, sufficient bending strength isachieved and the bonding strength between the internal electrode 12 andthe piezoelectric layer 11 is improved, while specific resistance of theinternal electrode 12 can be decreased so as to suppress the heatgeneration from the internal electrode 12 during continuous operation,thus making it possible to make the multi-layer piezoelectric actuatorhaving stable displacement of the device.

The present invention is not limited to the examples described above,and various modifications can be made to an extent that does not deviatefrom the scope of the present invention.

Example 4

Piezoelectric material powder constituted from lead zirconate titanatePb(Zr, Ti)O₃, having Curie temperature of 300° C. and particle size of0.7 μm, an organic binder made of butyral resin and a plasticizer weremixed to form a slurry which was formed into a green sheet 150 μm thickby slip casting method.

An electrically conductive paste, that included metal powder havingpredetermined composition of Ag—Pd component which would make theinternal electrode, an organic resin and a solvent, was applied to oneside of the green sheet to a thickness of 4 μm as shown in FIG. 2 byscreen printing process, so as to form the conductor pattern. Then 30pieces of the ceramic green sheet whereon the conductor pattern wasformed were stacked one on another. Then 5 pieces of the green sheetwithout electrically conductive paste printed thereon were stacked onthe top and bottom surfaces of the stack, thereby making the multi-layergreen compact having the construction shown in FIG. 2.

The multi-layer green compact was put into a die and was heated to 90°C. while applying a pressure of 100 MPa by means of an isostatic pressso as to be integrated.

The multi-layer green compact that had been integrated was cut into 10mm square and was heated to 800° C. for 10 hours to remove the binder,followed by firing at 1130° C. for 2 hours, thereby to obtain thepiezoelectric stack. Thickness of the piezoelectric layer thatconstituted the piezoelectric stack was 120 μm and thickness of theinternal electrode was 3 μm. The rate of cooling down from the maximumtemperature was set to t/3 (° C./minute) during firing, where t (° C.)is Curie temperature.

Then Ag-glass paste including Ag as the main component was applied to apair of opposing side faces of the active section and was heated at 750°C. for 1 hour before being cooled down at the rate shown in Table 5thereby to complete the heat treatment and form the external electrode.

Then the stack was immersed in an oil bath heated to 400° C. and a DCvoltage of 3 kV/mm was applied between a pair of external electrodes ofthis device for 1 hour so as to apply sufficient polarization treatmentto the crystal grains that constituted the piezoelectric layer and,while maintaining the voltage applied thereto, was cooled down to theroom temperature below Curie temperature, thereby to make themulti-layer piezoelectric element. Proportion of preferred orientationof the crystal grains was measured by X-ray diffraction methodimmediately after the polarization treatment and after continuousoperation of 10⁹ cycles. The change in the ratio of lattice constantsc/a is shown in Table 5. Effective piezoelectric strain constant wasevaluated by applying voltage of 0 to 200 V to a sample of themulti-layer piezoelectric element that was fastened onto avibration-isolated test bench with a load of 150 kgf applied thereto inthe stacking direction. Change in the length of the multi-layerpiezoelectric element was measured and was divided by the number ofstacked layers and the applied voltage. Curie temperature was determinedby measuring the temperature characteristic of the capacitance of thepiezoelectric porcelain. High-temperature durability test was conductedby using a thermostat and operating the device to undergo 10⁹ cyclesunder conditions of load of 150 kgf applied thereto at temperature of150° C. and frequency of 50 Hz.

Comparative example was made by applying the conventional polarizationtreatment to the multi-layer piezoelectric element described above.Crystal grain size was determined through observation under electronmicroscope.

TABLE 5 Effective High- Composition Average Change in piezoelectricCurie temperature of internal Polarizing grain degree of strain constanttemperature durability test No electrode condition size μm orientation(%) d₃₃ pm/V ° C. 10¹⁹ cycles *4-1  95/5 2 2.5 7 880 331 B 4-2 95/5 12.0 3 870 330 A 4-3 95/5 1 2.5 4 880 330 A 4-4 95/5 1 3.0 5 890 330 A4-5  85/15 1 2.5 4 910 330 A 4-6  90/10 1 2.5 4 900 331 A Note) A:Excellent, B: Good

Table 5 shows that samples Nos. 4-2 through 4-6 that were subjected tothe polarization treatment according to the present invention and showedchanges in the degree of orientation of crystal grains of thepiezoelectric material not larger than 5% demonstrated satisfactoryresults in the operation test of the present invention with changes indisplacement after continuous operation within 10%.

In sample No. 4-1, where the change in the degree of orientation waslarger than 5% after operation, change in displacement after continuousoperation exceeded 10% and reached 15%.

INDUSTRIAL APPLICABILITY

The present invention provides the multi-layer electronic component andthe method for manufacturing the same that are capable of suppressingdelamination from occurring between the ceramic layer and the internalelectrode, so as to provide the multi-layer piezoelectric element andthe injection apparatus that are excellent in durability.

1. A multi-layer electronic component comprising; a stack formed bystacking piezoelectric layers and internal electrodes one on anotheralternately and, a pair of external electrodes formed on two opposingside faces of the stack, wherein the internal electrode has a firstinternal electrode connected to the external electrode formed on one ofthe two side faces and a second internal electrode located between thefirst internal electrode and connected to the external electrode formedon the other one of the two side faces, and wherein the internalelectrodes and the piezoelectric layers are faced in proximity so that aspace between them is 2 μm or less over an area occupying 50% or more ofthe active region where the first internal electrode and the secondinternal electrode oppose each other.
 2. The multi-layer electroniccomponent according to claim 1, wherein a change in a degree oforientation of the crystal grains that constitute the piezoelectriclayer is within 5%.
 3. The multi-layer electronic component according toclaim 2, wherein an average grain size of the crystal grains of thepiezoelectric layer is 5 μm or less.
 4. The multi-layer electroniccomponent according to claim 3, wherein thicknesses of the piezoelectriclayers are 200 μm or less.
 5. The multi-layer electronic componentaccording to claim 1, wherein thicknesses of the internal electrodes are5 μm or less.
 6. The multi-layer electronic component according to claim1, the internal electrode including an inorganic component differentfrom the metal which is main component, wherein an average particle sizeof the inorganic component is smaller than an average grain size of thecrystal grains of the piezoelectric layer. 7-25. (canceled)